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KVM: x86: Decoding guest instructions which cross page boundary may fail

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Once an instruction crosses a page boundary, the size read from the second page
disregards the common case that part of the operand resides on the first page.
As a result, fetch of long insturctions may fail, and thereby cause the
decoding to fail as well.

Cc: stable@vger.kernel.org
Fixes: 5cfc7e0f5e
Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Nadav Amit 2014-10-03 01:10:04 +03:00 committed by Paolo Bonzini
parent 2bc19dc375
commit 08da44aedb
1 changed files with 4 additions and 2 deletions
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6
arch/x86/kvm/emulate.c
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@ -778,8 +778,10 @@ static int __do_insn_fetch_bytes(struct x86_emulate_ctxt *ctxt, int op_size)
static __always_inline int do_insn_fetch_bytes(struct x86_emulate_ctxt *ctxt,
unsigned size)
{
if (unlikely(ctxt->fetch.end - ctxt->fetch.ptr < size))
return __do_insn_fetch_bytes(ctxt, size);
unsigned done_size = ctxt->fetch.end - ctxt->fetch.ptr;
if (unlikely(done_size < size))
return __do_insn_fetch_bytes(ctxt, size - done_size);
else
return X86EMUL_CONTINUE;
}